drm/i915/cnl: Enable SAGV for Cannonlake.

For now inherit from previous platforms.

v2: Rebase on top of CFL.

Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170809205248.11917-2-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -3571,7 +3571,8 @@ static bool skl_needs_memory_bw_wa(struct intel_atomic_state *state)
 static bool
 intel_has_sagv(struct drm_i915_private *dev_priv)
 {
-	if (IS_KABYLAKE(dev_priv) || IS_COFFEELAKE(dev_priv))
+	if (IS_KABYLAKE(dev_priv) || IS_COFFEELAKE(dev_priv) ||
+	    IS_CANNONLAKE(dev_priv))
 		return true;
 
 	if (IS_SKYLAKE(dev_priv) &&